The present invention relates to an ink-jet print method and apparatus for printing an image on a printing medium using a printhead having a plurality of print elements (nozzles) that eject ink.
In recent years, color printers using various print schemes have been developed as color image output equipment. Of these printers, serial ink-jet printers that print in units of lines (bands) are popularly used owing to their merits, i.e., since they are inexpensive, can print high-quality images on a large number of kinds of print media, can be easily made compact, and so on.
Such serial printer forms a print image by developing print information for one scan (band) into image data to store the data in a memory, and driving the print elements of a printhead on the basis of the image data developed on the memory while scanning the printhead with respect to a printing medium. Among such serial printer apparatuses, a color printer apparatus that prints a color image using color inks is known, and as its printhead, a head prepared by arranging, in line, yellow, magenta, cyan, and black print element groups (nozzle groups) in a direction perpendicular to the scanning direction of the printhead is popularly used. In the printhead with this arrangement, the print element groups corresponding to the individual colors are arranged to be separated by given intervals to produce a delay time from when the print scan using one color print element group is complete for the printing medium until the print scan of print data of the next color is started. Also, the ratio of decrease in print speed attributed to the delay time is decreased. In this manner, color nonuniformity, smearing, and the like, which are produced between adjacent different color dots on the printing medium, can be eliminated, and a color output with high image quality can be realized.
In recent years, more printer apparatuses perform binarization processing for image data including multi-valued information per pixel like a picture image and output processed data. When such multi-valued data is converted into binary data, the size (dot area) of one pixel printed and its lightness determine the graininess of the image. More specifically, it is generally known that the graininess increases as the area (dot shape) of one pixel printed is larger, and as the lightness of the pixel is lower (its density is higher). As a technique for reducing the graininess in a printed image, the area of each pixel to be printed is reduced to increase the resolution of the printed image.
For example, a printer apparatus, which mounts both a print means that uses ink with a relatively high density and a print means that uses ink with a relatively low density and prints by selectively using the print means, has been proposed. In this printer apparatus, whether to print using one or both the relatively dark (thick) and light (thin) inks is determined in correspondence with the types of images to be printed.
Also, printer apparatuses which can be selectively used as a monochrome printer apparatus and a color printer apparatus by exchanging an ink cartridge that integrates a printer head and an ink tank, as is well known, are popular. Such printer apparatuses have been developed to realize both the enhanced monochrome function that can realize high-speed wordprocessing outputs, which are strongly demanded by users, and the function of outputting color graphics images. Such printer apparatuses detect the type of cartridge mounted currently, and execute, e.g., processing for switching the control for a monochrome cartridge and the control for a color cartridge. In existing printer apparatuses, the ink cartridge is exchanged to exchange color inks and monochrome ink.
In the field of color printing, various examinations have been made to improve the gradation characteristics of color graphics outputs. For example, the resolution for drawing is set to be higher than that in a normal color print mode to improve the drawing performance, or the resolution of the printer apparatus is increased to supply multi-valued data as print data to the printer apparatus and the multi-valued output is generated using subpixels. Such improvements have been conventionally made among such apparatuses, and have been put into practical applications in recent years.
Furthermore, in order to print a pictorial image using an ink-jet printer apparatus, a method of printing an image on a printing medium simultaneously using inks with a plurality of different dye concentrations has been conventionally proposed. That is, four or three inks, i.e., C, M, Y, and K, or C, M, and Y inks are normally used in a conventional printer apparatus, but two different inks having different dye concentrations are used for each of C, M, Y, and K, or C, M, and Y inks to perform printing. According to such print method, the color reproduction range can be remarkably broadened, and the graininess of the image can be greatly eliminated by printing an area with a high lightness (where dots are dispersed on the printing medium) in the image using ink with a low dye concentration. Conversely, a portion with a low lightness and high saturation is printed using ink with a high dye concentration that produces small graininess, thereby obtaining a high-color development image.
However, in the above-mentioned method, since a large number of different inks must be simultaneously set in the printer apparatus, the printer apparatus becomes a very complicated system. Since a general user performs monochrome printing most of the time, it is not efficient to always prepare inks with low dye concentrations, which are not frequently used, in the printer apparatus. Furthermore, since the printhead cannot have a predetermined size or more, its printable area must be reduced or the capacity per ink of the ink tank must be decreased.
In order to increase the resolution of print data in the conventional color printer apparatus, the storage capacity of a memory means (print buffer) for storing image data must also be increased. Normally, the print buffer comprises a RAM (random-access memory). Since the cost of such RAM is roughly determined in proportion to its memory capacity, an increase in storage capacity of the memory raises the cost of the apparatus.